Herbicide resistance in weedy plants is a growing problem in our world today and is threatening the utility of conventional agricultural practices. To illustrate this problem, today approximately 396 herbicide resistant weed biotypes have been identified comprising 210 species (123 dicots and 87 monocots). Of the 396 resistant biotypes, 139 have been reported in the United States. Additionally, 108 of the 396 resistant biotypes representing 38 species are resistant to two or more modes of action. Furthermore, 44% of biotypes with multiple herbicide resistance (MHR) have been documented since 2005.   

Producer complaints in 2006 from a malt barley production area in Montana led the Dyer and Menalled labs at Montana State University-Bozeman to investigate wild oat (Avena fatua L.) populations that were not controlled by tralkoxydim or pinoxaden. This complaint was unusual because it was the first year pinoxaden was commercially available, and due to its novel chemical characteristics, successful control was expected. We collected two populations and challenged them with field use rates of eleven herbicides in the greenhouse and confirmed that, in addition to pinoxaden and tralkoxydim, they are also resistant to the acetyl-CoA carboxylase (ACCase) inhibitors fenoxaprop, clodinafop, fluazifop, quizalofop, and diclofop. In addition, the populations are resistant to imazamethabenz and flucarbazone, members the acetolactate synthase (ALS) inhibitor herbicide family, as well as triallate, a carbamothioate herbicide that inhibits very long chain fatty acid elongation, paraquat, a PSI inhibitor, and difenzoquat, which has an unknown mechanism of action. Producers with these resistant weeds cannot control them with any of the selective herbicides used in cereal crops.

Overall, the occurrence of multiple herbicide resistant weed biotypes is on the rise and can cause significant crop yield loss, increase production cost, and threaten current weed management strategies. Therefore, the objectives of my research will strive to evaluate the molecular, physiological, and ecological aspects that confer multiple herbicide resistance in a wild oat population from Montana. The ultimate goal and outcome of this research is to disseminate our findings to provide information about a weed population’s response to intense herbicide selection from multiple herbicides and use this knowledge to inform producers and land managers on how to proactively and sustainably manage weedy plants. 


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